


An Omega's Place

by SinningfortheWinning



Category: Gravity Falls
Genre: Alpha Mabel Pines, Alpha/Beta/Omega Dynamics, Come Inflation, Dubious Consent, F/M, Futanari, Omega Dipper Pines, Sibling Incest
Language: English
Status: Completed
Published: 2020-09-30
Updated: 2021-02-14
Packaged: 2021-03-08 02:54:42
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 3,790
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26728528
Author URL: https://archiveofourown.org/users/SinningfortheWinning/pseuds/SinningfortheWinning
Summary: Dipper is an omega in a world where omegas are nothing but sex toys to breed with and Mabel is a horny alpha.
Relationships: Dipper Pines/Mabel Pines, Pacifica Northwest/Dipper Pines
Comments: 12
Kudos: 95





	1. Chapter 1

**Author's Note:**

> Sloppy work of Dipper getting used. Enjoy.

To Dipper, the room is shaking, jolting back and forth while the bed creaks and the sound of skin slapping skin surrounds him. To Mabel, the room hardly exists because her damn alpha hormones keep getting the better of her in the mornings.

Ever since they presented, Dipper as an omega and her as an alpha, their days have been spent testing how strong the bed frames are. Young alphas needed to get this out of their systems frequently, after all and as an omega it's Dipper's job to take every load she wants him to.

And man does Mabel want him to take a lot.

She got bigger than him, stronger and faster and hornier. Dipper stayed small, slow, and still got horny but most days Mabel was the only one getting off. It's alright though because as far as omegas go, he's treated good. Mabel will fuck him until he's sore and bulging from cum but outside of that they're just friendly twins.

Most alphas fuck their omegas and treat them like nothing but breeding machines, family or not. So Dipper is lucky Mabel is only aggressive during her ruts. And even then so long as he just lays there and takes it she never growls or bites him.

"This time we're going to get the knot in!" His twin sings. "Knot time for my bro-bro!" Her alpha cock is huge already and rams into Dipper deeper than anything probably should and her knot only makes that worse.

"Ah Mabel, can we skip the knot this time? You did it last night and my butt still hurts." Dipper looks back at his twin with pain in his eyes. "Besides I'm not in heat so it's not like it's going to do anything."

"Oh but dippin dots it feels good! Besides, we don't want my cum to go to waste! It's better for it to stay all in your tum-tum!" She sticks her tongue out at Dipper and rams her dick into him really hard just to show that she's not going to back down. "And imagine if you were in heat! We have to practice for when it comes!"

Dipper groans, the sound of it choppy because his sister's hips are bumping into his so hard. "Fine but don't cum so much this time. I still have a lot in me from last night." His stomach is in a constant state of flabby because Mabel cums in him at least twice a day.

During her ruts his skin actually develops some stretch marks from how much she unloads into him. And those happen once a month so his body is pretty constantly full of cum as a good omega's should be.

"You get what you get and you don't throw a fit," his twin giggles. Her cock jerks inside of him and Dipper can feel it expanding more with the knot. "Get ready, dippin sauce! I'm ready to bust a nut in your cute lil' butt!"

Dipper rolls his eyes and grunts loudly when the knot is forced into his ass. A shiver crawls over his limbs as hot cum floods his body. Mabel clearly isn't holding back like he asked but all he can really do is lay there and wait for her to finish.

"Oh shoot, I forgot I told Pacifica that she could come over today!" Mabel's still twitching cock isn't even done filling Dipper up when she stands, the knot forcing him up with her. "And here I am with my dick out," she says in a silly voice.

"M-Mabel! Just because you can walk around like this doesn't mean you should! It hurts!" Dipper's legs are dangling down and he has to lean his back on her chest to keep from being folded in half while his twin walks from the bed to the dresser to find a dress. "And you fucked and knotted me even though Pacifica is coming over? Come on, this is embarrassing!"

"It's nothing she hasn't seen before," Mabel snorts. "She's had her knot in you too so it's not like she has any room to judge us for being too horny to keep it to ourselves this morning." She doesn't bother wrapping an arm around Dipper to help hold him up as she trots out to the living room.

Their parents are at work so they have the house to themselves which is good because it's always so embarrassing to come downstairs bloated from cum. Their mom is also an omega though so she's often full too.

"There she is!" Mabel sings when there's a knock at the door. The blonde laughs as soon as the door is open, poking Dipper's bulging stomach.

"Damn, can't even take a load without turning into a balloon," she teases. "I bet I have a load big enough to like, totally ruin his stomach today." She rubs his round stomach with one hand and her growing cock under her skirt with the other. "You just knotted him huh?"

"Yeah, but Dipper knows how to swallow! I've trained him to be the best omega around!"

That's all Pacifica needs to hear too pull her panties down and free her large alpha cock. They've barely closed the door and already she's trying to get inside of him. She grabs his hair and leads his head to her cock, which he has no choice but to start choking down. It's got to be a good fourteen inches and it's so thick that his jaw creaks trying to take it all in. Mabel is bigger though so he can do this.

She keeps a strong grip on his hair as she forces her dick down his throat, laughing at the way he's gurgling. Dipper lets his limbs dangle uselessly while the alpha begins to use his throat. Mabel is still in his ass and will be for a while so he's stuck between the two of them until they're finished with him.

Pacifica holds him by the sides of the head to keep him in place, her pelvic bone slamming into his nose with every thrust. "So today that weird beta called me again," she says casually to Mabel.

"Oh my gosh, no way! What did he say?" Mabel is firmly holding Dipper's hips in place against her own so that get friend can have her fun.

"Said he would be willing to buy one of those breeding straps that like, ties the bitch onto you so you can just keep your dick in them. He wants it so bad but I came in him once and he couldn't even take it all. I need an omega, I think."

"You do! Omegas hold cum so easy! I should get one of those straps for Dipper. Mom said I should try not to breed him too early but she's an omega, she doesn't get it! I see an omega that needs to be filled and I fill them!" Mabel laughs, rubbing her hand on Dipper's ass. "And just think of how many pups he can pop out!"

Pacifica nods. Her cock is still reaching deep in his throat, well past his collar bone, ramming into him and not allowing much time for him to breathe. "Next time he's in heat just go in his room and do it. If you don't your dad probably will soon anyway. He's at a good breeding age. I fucked my cousin full of a brat because her dad was taking like waaay too long. I think they should be bred when they present."

"Yeah, I got that omega girl at school knocked up. She took it like a champ even though I kinda surprised her with it. But how was I supposed to resist! She smelled nice and no one else was doing it!" Mabel puts one of her hands on the back of Dipper's head to make sure he's swallowing Pacifica's cock all the way to the base. "I think his next heat I'll do it."

The blonde laughs and thrusts harder into Dipper's poor jaw. "Good. Little omega bitch needs pups up his ass to know his place. Now swallow all I got for you like a good omega." Dipper's cheeks puff up as her knot is pushed into them. She's done this before and gotten stuck there and this time doesn't seem like she'll be able to pull back out either.

Hot cum pours directly down his throat and he has no choice but to gulp around her throbbing dick as it fills him more and more. With Mabel's loud in there already, it's only making his stomach grow bigger and bigger.

"Ah, I've been holding this one in all day. I had a feeling you'd let me use him. When our knots go down you wanna switch holes? I think I can drain a few more loads into him while we chat."

"Of course! Use him all you want! I haven't fucked his little throat in a while anyway, it'll be nice to feel it again."

The girls continue to talk, Dipper stuck between them like a roasting pig, skewered and stuffed before a feast. All the talk of breeding him excites him because he's a good omega. If Mabel or any alpha wants to fuck a litter into him then he'll lay there and take it. As good omegas should.


	2. Chapter 2

**Notes for the Chapter:**

> Another kink request for this fic.

Everything is going according to plan. Mabel planned her parents a nice weekend getaway right over Dipper's heat. They paid attention to his hear cycles most months but this one Mabel was able to throw them off and get them out of the house.

Now her and Dipper are left alone in the living room, her omegan brother wiggling in his seat from the oncoming heat. She can tell he's already hard and her nose is hungrily taking in the faint smell of slick coming from his hole.

"Ahh, Mabel I think I need to go lay down. My stomach hurts." Dipper is sweating and rubbing his head, his body covered in blush.

"Nope! Dr. Mabel actually has the best medicine around to help out that tummy ache!" She grabs her small twin by the wrist and leads him into her lap so that he's straddling her wide hips. He let's out a whine and Mabel tsks at him. "None of that bro bro! You know you're at a good age to breed! Just let me get a few loads in there, please?"

She gives him her puppy dog eyes while moving his hips against hers. Mabel's much bigger cock is straining against her way too short shorts, grinding against Dipper's harshly. Soon enough he's going to be begging for cock anyway but Mabel has to play nice until his heat fully kicks in.

"We're going to have so many pups. I'm going to pump you full of one right after the other!" Mabel is giddy and already grabbing Dipper's clothes to pull them off. The omega isn't fighting back at all but he's also not helping. Luckily for him Mabel is so eager to finally breed him that she doesn't mind stripping them both.

As soon as he's naked and sitting back on her lap, Mabel reaches behind him to feel how much slick is coming out. The thick, hot and sticky fluid coats her hand and she's unable to stop herself from quickly lining up her dick and shoving it up his ass.

It's so wet and it's never been this hot before. "Oh, Dipper! This feels so good!" she moans loudly. "I'm going to fuck this little butt until it's full of pups!" Mabel's body knows that the sooner she fucks into him the sooner he'll get knocked up so she grabs him by the hips and starts to bounce him on her cock.

Dipper can only whimper and drool thanks to his heat. It's like the heat melts their brains into perfect sex toys and Mabel loves it.

Her cock is already throbbing against Dipper's insides, singling his body to start tensing up. Mabel is moaning loudly and grunting every time Dipper's ass clings to her cock, surely loud enough for the neighbors to hear.

"Oh, here it comes! Get ready, I saved up a lot of liquid love for you Dip!" She cries out loudly and slams him down into her dick as hard as she can so that her knot can force its way inside of her twin. Hot cum gushes out into his stomach and Dipper shudders as it fills him. His belly swells a little and as Mabel comes down from her orgasm she realizes that Dipper has a better chance at getting bred if there's more cum.

A quick text tells Pacifica that Dipper is in heat and that she should come over to fuck him. The blonde is totally up for the challenge and tells her she'll be there as soon as she's done putting groceries away.

"You'll get two whole alphas in you today! You're going to have a whole litter thanks to me and Pacifica." Mabel pats Dipper's ass and her twin groans. He's slumped over and his body is satisfied for the moment with her knot firmly in his ass.

Waiting for it to go away is fine with Mabel because by the time she's able to start moving again Pacifica is walking in. She's in a short skirt and a crop top, no bra or underwear to be seen. Her nipples stand perky under the white fabric and her growing cock lifts the black skirt up with it.

"You've already got a load in him, nice. Let me squeeze in there and we'll see how long he lasts with both our cocks." She sits on the couch with Mabel and the two alphas hold Dipper between them while Pacifica lines up her dick.

Dipper's hole has taken a lot over the years. Nearly every alpha he knew has fucked him at least once. Even their teacher once held him after class to get a piece of his ass in exchange for a higher score on an essay.

But taking both Pacifica's and Mabel's cock at the same time is stretching it farther than it's been praise pushed before. His slick and eager body help a lot but even with Mabel and Pacifica pushing down on his shoulders it's a slow process.

"Omegas are so small. It feels so fucking good but I just want to be in him already!" Pacifica growls and digs her nails into his hips, forcing them down as Mabel pushes on his shoulders. Her twin whimpers loudly but both cocks are now snuggly in his asshole.

"Oh wow! This feels awesome!" Mabel starts to grind into Dipper and Pacifica does the same. "Thanks for coming, it feels really nice doing this with you. I know he's going to pushing out lots of pups thanks to us!"

"Oh yeah, we're not stopping until he finally gets the breeding he's deserved. I'm glad you made sure this could happen, if you didn't I was just going to tie him to your cock until he got knocked up."

Mabel laughs and pats the top of Dipper's head. He's out of it now that his body is being pushed to a limit he's never had to face before. "I know, my mom was always so picky about when he should have pups though. Now she'll come home to a very pregnant omega."

Pacifica nods and doesn't answer other than that because she's moving faster and focusing on getting to shoot a load into Dipper as well. Both her and Mabel are hugging now to keep Dipper in place and the obscene wet noises coming from his ass are muffled between them.

They growl when they cum and Dipper takes not one knot and stream of cum but two. It's so much all at once that he passes out before his stomach can finish swelling.

Him being out cold doesn't stop either alpha. Mabel and Pacifica go on about their days while they fill him with as much cum as their bodies allow.

Mabel has no idea how much time has passed when he looks like he's about to burst but the three of them are all very sweaty now. His stomach is so large they have to lean back a bit while they continue to fuck him. Dipper has been in and out of consciousness the entire time but looks happy about being knocked up.

Pacifica is close to coming again and so is Mabel and she's pretty sure it'll be their last time for a little while. They work their hips up into him until their knots pop into his red, swollen hole and begin to pump more of their seed into him.

It's quiet at first but then Dipper coughs and makes a sour face as if he's tasted something tart. He clamps his mouth shut only for cum to dribble out of his nose and over his hand.

"Lucky you, we're done for now," Pacifica laughs before laying back. Mabel lays back on the couch too and Dipper is stuck between them trying to rub the cum from his nose. "Wow, we really did a number on him. At least we know for sure that he's got enough cum in him to knock him up."

"More than enough! I'm so proud of us. Go team!" Mabel puts her fist in the air triumphantly but it falls back by her side quickly thanks to how tired she is. "I need a nap now. Maybe a day long nap. Yeah, that sounds good." Mabel lets her eyes fall shut, ready to sleep now that she's made sure Dipper is going to have her pups.

**Notes for the Chapter:**

> Happy new year


	3. Chapter 3

**Notes for the Chapter:**

> Plenty of people requested this one.

There's still time to fuck Dipper during his heat and Mabel intends to pump as many loads into him as she can while he's fertile. Pacifica reminded her that she could tie him up on her cock so that the only way her cum could go is up into him.

The blonde is nice enough to go to the nearest sex shop to get her a harness for him and as soon as Pacifica leaves to go find another omega to fuck pups into Mabel is wrapping Dipper up in the harness. It wraps around his whole body and ties his arms and legs behind her.

She makes it so his belly is facing away from her because it's too full to be pressed up against her. Once the black straps are tightly binding Dipper to her, her large alpha cock buried deep in his ass, Mabel walks to her room to test it out. Each step bounces him on her dick but keeps him from falling and it's such a hot fucking sight that by the time she makes it up the stairs she's coming in him again.

Dipper is her personal flesh light now and his warm little body is going to be tied to her for days even after his heart.

She stands in front of her body length mirror in her room, admiring how Dipper is just a belly and a face with black straps holding his arms by his sides and behind her back. His legs are back there too, giving him no way to possibly escape.

"This is a good look for us Dip! Look at this full belly! Our litter of pups is going to be a big one!" She pats his large stomach and Dipper makes a grumbling noise. "Don't pout, you'll get to pump my pups out for the rest of our lives with this neat thing!"

Mabel walks over to her bed and grabs a dildo gag from her nightstand to shove into Dipper's mouth. "Can't have my cum spilling out of here too much." She ties it around the back of his head then lays on her back with her phone out.

She snaps a picture of the new set up to send to Pacifica and a few others then puts on some porn. It's a nice video of an alpha fucking a pup into his newly presented omega daughter. He's growling, biting, and holding her down while she whines about taking it so rough.

"See I could've been like this when we presented but instead I waited way too long to get you in heat. Mom is lame for making us wait." Just the smallest hip movements give her enough friction to get off to the porn, pumping another load into Dipper.

Her twin has ballooned to a good size and with his throat mostly closed from the toy her cum only makes him bigger. Still, a bit of it dribbles from the corner of his mouth and she sighs.

"C'mon, swallow it back down like a good boy. There you go, good omegas want every drop of their alphas cum in them, Isn't that right?"

Dipper works his clogged throat to swallow and nods. His heat is making every bit of praise feel good and he starts to fuck himself on her cock to please his alpha.

"Oh yeah, move just like that. Deeper!" Mabel thrusts into her twin over and over until more cum is forcing its way into him. "Ahh you're a good omega, Dipper. You take cock like a champ!"

With him tied to her, Mabel is able to get off every second that her body is ready to while she's still able to do what she needs to. Cleaning her room, making food, all that stuff gets done while her cock rests in Dipper.

When their parents come home and see Dipper asleep on her, Mabel rubbing his big belly, they only sigh and get used to the fact that soon Dipper will be having her pups. She smiles and starts to fuck him again, not caring that his heat ended a day ago. Having her cock constantly buried in his warm hole is too good to pass up and she doesn't really have plans to take him off any time soon.

Eventually she'll need to but omegas are durable little fleshlights. And he has the gag in still so it's not like he can say anything about it. He just has to stay there with a cock in his ass, taking every load she gives.

Mabel is sure to take pictures to send to Pacifica and other friends so they can see just how much cum she's pumped into him. They congratulate her on it and mention how they'd like a turn once he's off the straps. Mabel has no problem with sharing and hopes that from now on Dipper will be constantly full of dick, cum, and pups. 

**Notes for the Chapter:**

> If he wasn't pregnant before he is now.
> 
> What else should Mabel do to her poor little omega brother?

**Author's Note:**

> I take kink requests, but I don't always accept them all. Nothing too long please.


End file.
